Methodology

To identify the most urgent global challenges the Global2015 survey uses the following criteria:

existential importance for life and the needs of many people (i. e.[that is] damages and risks to life, health, to their natural foundations or to their economic base)

mainly man-made causes, resp.(respectively) options for humans to avoid impacts or to improve the situation (for instance, if a huge meteorite would strike, it would be quite small)

impacts for affected people are not mainly caused – or could not mainly be minimized – individually by themselves (such as tobacco use) but by other human beings or larger human activities.

The challenges are differentiated according to the kind of possible action or measures for tackling them. Therefore, some similar issues are combined (e. g.[for instance] epidemics), while others are not (e. g., indoor and outdoor air quality may be similar problems, but require very different measures). Additionally, data availability has a great influence on the differentiation of challenges, too, because most available data is aggregated to specific issues.

Further selection and especially weighing of global challenges are based upon the following:

damages and risks to human life (death cases)

health losses

damages and risks to natural foundations of human life

economic damages

number of affected people.

Unfortunately, to none of the quantities data for all the challenges described is available. Therefore there is no common single measurement for all challenges, especially not for those of inherent high risks or increasing damages. However, for most of the challenges, data on several quantities is available, hence the challenges are linked by several measurements of comparison.

Weighing the challenges is done by combining data on the extent and the severity of the challenges. The following six indicators combined cover all challenges (with each of the first two covering the majority of challenges):

number of affected people

current death cases

future death cases at risk

affected natural foundations (portion of global resources)

current economic losses

future economic losses at risk.

These indicators are shown in small diagrams below the headline of each challenge.

To be combined, the six quantities should have a similar scale and dimension. This is important to obtain a similar influence of each indicator on the result of their combination. To reach this comparability, a statistical method called "standardizing" or "z-score" could be applied. However, this would transform real data into quite artificial numbers, but more importantly, would make it very complicated for the reader to check the applied combination of data. It would be necessary to calculate all values of all challenges by a complex, computer-driven procedure even to check the weighing of a single challenge. Instead of the standardizing method, a simpler operation with a similar effect is used:
The quantities are transformed into per cent data. Each value of an indicator is here relative to the highest value of the same indicator. For instance, the maximum number of people affected by indoor air pollution is 3 billion, or 3 000 million. This is set to be 100%. Now, 300 million people are affected by unsafe birth conditions. Hence they represent 10% (compared to the challenge with the highest number of affected people). As a calculation:
(300 / 3 000) x 100 = 0.1 x 100 = 10%
This way we can make all quantities comparable by ranging from 0% to 100%.
Now the percentages are simply added for each challenge. Hence, the higher the percentages of death cases, affected people, economic losses etc.(and so on) in comparison to other challenges are, the higher is the resulting total value – indicating the relevance.

The global challenges are presented in the order resulting from this combined indicator. In the calculation process described above three exceptions are made, as you can see in the following overview:

1 By deliberate intent, the numbers of current death cases and of future death cases at risk are considered as the most severe and important indicators and therefore weighed double.
2 The percentage of future deaths at risk is related to the maximum of current deaths instead of future deaths. This ensures that future death cases at risk do not count more than current death cases, which would happen otherwise. (The given maximum value of lives at risk is much lower than the maximum of current deaths if based on the same period of time.)
3 The numbers of affected natural foundations are already given in percentages (portion of global resources, e. g. 33% of global agricultural land). Since there is unfortunately only very little data available, its influence should be kept minimized. This is done by not upscaling it to a maximum of 100%.

Furthermore, regarding the indicator on future economic losses its maximum value is – in contrast to all its other values – given as a percentage. Also, the value is related to a time frame of several years. In lack of specific information it is assumed to be 12.5% of global GDP(gross domestic product) in current terms for a time frame of 20 years. (A higher value would make no big difference.)

The simplified method described above delivers similar results as other methods, that are statistically more sophisticated, but less transparent.
If you want to check the combined indicator of a challenge in the survey, just take the data shown in the small diagrams below the headline of the challenge, and the highest values of the same indicators. Then use these values in the calculation described in the overview above (calculate the percentages accordingly and add them). The same way allows you to compare the aggregated values of two or more challenges.

Despite all methodological considerations, it has to be strongly emphasized that due to lack of data, as described, and because the quality of available data usually is not very good, the resulting order of challenges cannot be very precise. The challenges fit together into groups with high, middle and lower relevance. The scale can only be blurred. Therefore, the order is not a matter of rank 5 or 6, but more a matter of rank 5 or 10. Because of these reasons, inter alia, we do not use numbers for ranking the challenges. Nevertheless, the real data shows very clear differences between the challenges indicating higher or lower relevance. This is visualized by the small diagrams below each challenge title.

Trend data is quite rare and mostly refers, like targets usually do, to the number or the proportion of affected people (resp. to the proportion of affected natural foundations of life). The trend symbols +, 0 and − in the survey always refer to the latest development in the available trend data (while + means that progress in reaching a target or improving the situation is made, which usually is not identical to an increase in quantity).

The challenges are inter-linked and often overlap each other and some are driving factors to others. Especially those challenges that have increasing impacts or large risks are underlying causes of several challenges that encompass larger current impacts. A graph of the World Health Organization – whose reports are an important base of this survey – shows more in detail the interconnections between some of the challenges: